Image sensors are provided with sensing elements which provide a potential well or depletion region in a substrate. Color filter arrays having patterns of color are selectively formed over the sensing elements. Light passes through these colored patterns and causes charge to be collected in the potential wells.
Color filter arrays are generally classified into two types, i.e., primary color type array employing red, green, and blue (RGB), and complementary color type filter array employing white, yellow, and cyan (WYC), or white, yellow, cyan, and green (WYCG), or the like. In the WYCG of like part-primary, part-complementary color filter array, good color reproduction is unattainable unless the spectral characteristics of the primary color coincides with one which is to be set up when those of two complementary colors are superimposed.
Color filter arrays are presently fabricated on top of photoelectronic sensors by patterning a diazo resin or other suitable binder containing a cationic mordant. The pattern is then subjected to a solution of an anionic dye. This results in dye incorporation into the pattern due to the binding of the anionic dye to the cationic mordant site. The full color filter array requires multiple layers of these dyed patterns so overcoating is necessary. Since the same type of resin is used for each layer, all dyes also have to be anionic in nature. This has caused problems in some instances where a dye is not bound tightly enough to the mordant. During the overcoating of the next layer of resin some of the dye is leached out causing less than optimum dye density and non-uniform dye density across the pattern. When this next layer is patterned there are always some areas of the underlying dyed pattern left exposed. This results in unwanted cross-dyeing caused by the uptake of the second dye in these uncovered areas.
This problem can be circumvented by intermediate treatment of the dyed pattern before coating the next layer. This treatment is meant to act as a barrier to dye leaching thus preventing cross-dyeing. However, this treatment involves at least one additional coating step to apply the material and often further treatment is necessary before the second resin layer can be applied. Examples of such barrier treatments are disclosed in U.S. Pat. Nos. 4,315,978; 4,355,087; and 4,357,415.
A method for eliminating the cross-dyeing problem was described in U.S. Pat. No. 4,580,159. It also involved the use of alternating layers of dye binders differing in their dyeing properties. This case differs from the present invention in that one was hydrophilic and the other hydrophobic. The hydrophilic layers were dyed by immersing in solutions of acid dyes and disperse dyes were heat transferred into the hydrophobic binders.
Although this method should indeed prevent cross-dyeing, it also involves the use of organic solvents for the coating of the hydrophobic layers. This is undesirable since organic solvents cause environmental safety and disposal problems that would not be encountered with an all hydrophilic system. Also, the dye density and uniformity produced by a heat transfer method of dyeing are not as controllable as with solution dyeing of hydrophilic layers to saturation.